COPENHAGEN -- Tens of thousands of protesters marched through the streets here Saturday, demanding bolder action on climate issues from the international negotiators who remain divided over how to reconcile differences between industrialized nations and major developing countries.

The protest was the largest of its kind since the U.N.-sponsored talks began in the Danish capital on Monday: Organizers said as many 100,000 people joined in the event, although police put the number at about 40,000.

Toward the end of the rally, police arrested 600 to 700 people after some activists began throwing cobblestones through windows and a handful of masked protesters set off small explosives near a group of government buildings.

On a day when little progress was made in the climate talks, activists spread out on foot across the city holding banners in English reading, "There Is No Planet B," and rocking back and forth inside a long ring of fabric that constituted a human boat, complete with a sail. Many had the number 350 -- which stands for an atmospheric concentration of carbon equivalent to 350 parts per million, the more stringent climate target many scientists embrace -- sewn or printed on their hats and clothes.

Billed as a crusade for "climate justice," the march was led off by members of indigenous groups to highlight how activists say global warming is affecting some of the world's most vulnerable citizens. Companion vigils were held in as many as 3,000 other locations worldwide, including Papua New Guinea, Israel, Japan and Saudi Arabia.

"What was going on in Copenhagen is deeply connected to people outside this absurd bubble of the conference, who have their hope pinned on the outcome of what happens here," said Bill McKibben, who founded the environmental group 350.org and took part in the demonstration. "The people outside the talks, out in the streets, know more about the issue than most of the people inside the conference hall."

According to one bystander, who spoke on the condition of anonymity because he is involved in the climate talks, masked, black-clad activists set off several explosives along Copenhagen's main canal, which is near several ministry buildings.

"They were lobbing them by the buildings," he said, adding that he saw flares first but that those were followed by "a couple big explosions."

The police kept the protesters from getting too close to the Bella Center, where the talks were going on. Several key factions, including the European Union and Japan, joined the United States in objecting to language in a draft U.N. proposal that requires developing countries to cut emissions only if those actions are funded from overseas. Citing the emerging economies' rising carbon output, the industrialized nations want them to commit to binding reductions as part of a political deal.

China's chief climate negotiator, Su Wei, told reporters Saturday that his country was simply sticking to the Bali Action Plan that negotiators agreed to in 2007, calling it "quite clear."

But Daniel M. Price, who as the White House's international economics adviser helped lead climate negotiations under President George W. Bush, said in an e-mail that rich nations "are well within the bounds of the Bali Action Plan in pressing for binding commitments from a small number of large emerging countries with very high greenhouse gas emissions. That this issue remained open for consideration was well understood at the time of Bali, immediately after, and then reinforced by all of the G-8 Leaders in their 2008 declaration in Hokkaido when they made clear their expectations that the mitigation actions of major developing countries would need 'to be bound' in a new international climate treaty."

Still, Alden Meyer, who directs strategy and policy for the Union of Concerned Scientists, said that U.S. officials are "trying to shift the negotiating goalposts in the last week of a two-year-long negotiating process" and are unlikely to have more success than the Bush administration in getting nations such as China and India to agree to binding cuts.

As the impasse continued -- and with many participants having little to do -- people inside the convention center gathered around televisions throughout the afternoon to watch the march.

But the protest did not seem to draw the attention of key officials such as Wei. Asked whether he thought the demonstration was having a constructive impact on the international deliberations, he replied in English, "Actually, that is something that I was not aware of."

He then continued in Mandarin, saying, "Because the venue is large, I cannot hear what is happening outside." He said that whether the march was hurting or helping depended on one's perspective.

"It shows the concentration of the general public and different sectors on the subject of climate change," he said. On the other hand, he added, "You can also say that they disrupt the negotiations, or the freedom of other people."